It is well known to employ surface finishing techniques to improve the surface finish and fatigue cycle life of metallic articles. Examples of such surface finishing techniques include shot peening and vibrofinishing.
Shot peening involves directing a stream of steel, ceramic or glass peening media at the surface of the article. The impact of the peening media on the surface introduces compressive residual stresses into the surface layer of the article. These compressive residual stresses improve the high cycle fatigue strength of the article.
Vibrofinishing, on the other hand, involves immersing the article in a container together with a polishing mixture. The polishing mixture is typically made from polishing chips (usually plastic or ceramic), an abrasive paste and water. Vibration of the container causes the polishing mixture to flow around the article, resulting in removal of material from the surface of the article. The vibrofinishing process typically employed to reduce the surface roughness of an article, for example to improve aerodynamic performance of a turbine or compressor blade.
Shot peening and vibrofinishing processes are often applied to the same article in sequence. This can be time consuming.
Vibropeening is a surface finishing technique that combines the improvement in residual compressive stress provided by shot peening, with the reduction in surface roughness provided by vibrofinishing. This combination makes the vibropeening process quicker and more cost effective than the prior art combination of shot peening and vibrofinishing.
In the vibropeening process, the article to be processed is immersed in a trough, which is filled up with a stainless steel media, and vibrational energy is provided to the trough. Additionally, the article may be rotated within the trough to further increase the level of interaction between the media and the surface of the article.
FIG. 1 illustrates a typical vibropeening apparatus 10 according to the prior art. The vibropeening apparatus 10 comprises a housing 20 within which is located a mounting frame 30 having a motor drive 40. The housing 20 accommodates a vibropeening bed 50 with the article 60 to be vibropeened being attached to the mounting frame 30 and suspended within the vibropeening bed 50. The motor drive 40 rotates the article 60 within the vibropeening bed 50.
However, a problem occurs with the vibropeening process when the article that is being processed has a large and particularly irregular geometry. In such situations, the vibropeening process may result in the component having low peening intensity, irregular peening treatment across the surface of the article, and, in worst cases, high distortion.